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queue.h

/*    $Id: queue.h 275 2006-06-30 20:21:15Z phk $ */
/*    $NetBSD: queue.h,v 1.45 2006/03/07 17:56:00 pooka Exp $     */

/*
 * Copyright (c) 1991, 1993
 *    The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *    @(#)queue.h 8.5 (Berkeley) 8/20/94
 */

#ifndef     _SYS_QUEUE_H_
#define     _SYS_QUEUE_H_

/*
 * This file defines five types of data structures: singly-linked lists,
 * lists, simple queues, tail queues, and circular queues.
 *
 * A singly-linked list is headed by a single forward pointer. The
 * elements are singly linked for minimum space and pointer manipulation
 * overhead at the expense of O(n) removal for arbitrary elements. New
 * elements can be added to the list after an existing element or at the
 * head of the list.  Elements being removed from the head of the list
 * should use the explicit macro for this purpose for optimum
 * efficiency. A singly-linked list may only be traversed in the forward
 * direction.  Singly-linked lists are ideal for applications with large
 * datasets and few or no removals or for implementing a LIFO queue.
 *
 * A list is headed by a single forward pointer (or an array of forward
 * pointers for a hash table header). The elements are doubly linked
 * so that an arbitrary element can be removed without a need to
 * traverse the list. New elements can be added to the list before
 * or after an existing element or at the head of the list. A list
 * may only be traversed in the forward direction.
 *
 * A simple queue is headed by a pair of pointers, one the head of the
 * list and the other to the tail of the list. The elements are singly
 * linked to save space, so elements can only be removed from the
 * head of the list. New elements can be added to the list after
 * an existing element, at the head of the list, or at the end of the
 * list. A simple queue may only be traversed in the forward direction.
 *
 * A tail queue is headed by a pair of pointers, one to the head of the
 * list and the other to the tail of the list. The elements are doubly
 * linked so that an arbitrary element can be removed without a need to
 * traverse the list. New elements can be added to the list before or
 * after an existing element, at the head of the list, or at the end of
 * the list. A tail queue may be traversed in either direction.
 *
 * A circle queue is headed by a pair of pointers, one to the head of the
 * list and the other to the tail of the list. The elements are doubly
 * linked so that an arbitrary element can be removed without a need to
 * traverse the list. New elements can be added to the list before or after
 * an existing element, at the head of the list, or at the end of the list.
 * A circle queue may be traversed in either direction, but has a more
 * complex end of list detection.
 *
 * For details on the use of these macros, see the queue(3) manual page.
 */

/*
 * List definitions.
 */
#define     LIST_HEAD(name, type)                                 \
struct name {                                               \
      struct type *lh_first;  /* first element */                 \
}

#define     LIST_HEAD_INITIALIZER(head)                           \
      { NULL }

#define     LIST_ENTRY(type)                                \
struct {                                              \
      struct type *le_next;   /* next element */                  \
      struct type **le_prev;  /* address of previous next element */    \
}

/*
 * List functions.
 */
#if defined(_KERNEL) && defined(QUEUEDEBUG)
#define     QUEUEDEBUG_LIST_INSERT_HEAD(head, elm, field)               \
      if ((head)->lh_first &&                               \
          (head)->lh_first->field.le_prev != &(head)->lh_first)   \
            panic("LIST_INSERT_HEAD %p %s:%d", (head), __FILE__, __LINE__);
#define     QUEUEDEBUG_LIST_OP(elm, field)                              \
      if ((elm)->field.le_next &&                           \
          (elm)->field.le_next->field.le_prev !=                  \
          &(elm)->field.le_next)                            \
            panic("LIST_* forw %p %s:%d", (elm), __FILE__, __LINE__);\
      if (*(elm)->field.le_prev != (elm))                   \
            panic("LIST_* back %p %s:%d", (elm), __FILE__, __LINE__);
#define     QUEUEDEBUG_LIST_POSTREMOVE(elm, field)                      \
      (elm)->field.le_next = (void *)1L;                    \
      (elm)->field.le_prev = (void *)1L;
#else
#define     QUEUEDEBUG_LIST_INSERT_HEAD(head, elm, field)
#define     QUEUEDEBUG_LIST_OP(elm, field)
#define     QUEUEDEBUG_LIST_POSTREMOVE(elm, field)
#endif

#define     LIST_INIT(head) do {                                  \
      (head)->lh_first = NULL;                              \
} while (/*CONSTCOND*/0)

#define     LIST_INSERT_AFTER(listelm, elm, field) do {                 \
      QUEUEDEBUG_LIST_OP((listelm), field)                        \
      if (((elm)->field.le_next = (listelm)->field.le_next) != NULL)    \
            (listelm)->field.le_next->field.le_prev =       \
                &(elm)->field.le_next;                      \
      (listelm)->field.le_next = (elm);                     \
      (elm)->field.le_prev = &(listelm)->field.le_next;           \
} while (/*CONSTCOND*/0)

#define     LIST_INSERT_BEFORE(listelm, elm, field) do {                \
      QUEUEDEBUG_LIST_OP((listelm), field)                        \
      (elm)->field.le_prev = (listelm)->field.le_prev;            \
      (elm)->field.le_next = (listelm);                     \
      *(listelm)->field.le_prev = (elm);                    \
      (listelm)->field.le_prev = &(elm)->field.le_next;           \
} while (/*CONSTCOND*/0)

#define     LIST_INSERT_HEAD(head, elm, field) do {                     \
      QUEUEDEBUG_LIST_INSERT_HEAD((head), (elm), field)           \
      if (((elm)->field.le_next = (head)->lh_first) != NULL)            \
            (head)->lh_first->field.le_prev = &(elm)->field.le_next;\
      (head)->lh_first = (elm);                             \
      (elm)->field.le_prev = &(head)->lh_first;             \
} while (/*CONSTCOND*/0)

#define     LIST_REMOVE(elm, field) do {                          \
      QUEUEDEBUG_LIST_OP((elm), field)                      \
      if ((elm)->field.le_next != NULL)                     \
            (elm)->field.le_next->field.le_prev =                 \
                (elm)->field.le_prev;                       \
      *(elm)->field.le_prev = (elm)->field.le_next;               \
      QUEUEDEBUG_LIST_POSTREMOVE((elm), field)              \
} while (/*CONSTCOND*/0)

#define     LIST_FOREACH(var, head, field)                              \
      for ((var) = ((head)->lh_first);                      \
            (var);                                          \
            (var) = ((var)->field.le_next))

/*
 * List access methods.
 */
#define     LIST_EMPTY(head)        ((head)->lh_first == NULL)
#define     LIST_FIRST(head)        ((head)->lh_first)
#define     LIST_NEXT(elm, field)         ((elm)->field.le_next)


/*
 * Singly-linked List definitions.
 */
#define     SLIST_HEAD(name, type)                                \
struct name {                                               \
      struct type *slh_first; /* first element */                 \
}

#define     SLIST_HEAD_INITIALIZER(head)                          \
      { NULL }

#define     SLIST_ENTRY(type)                               \
struct {                                              \
      struct type *sle_next;  /* next element */                  \
}

/*
 * Singly-linked List functions.
 */
#define     SLIST_INIT(head) do {                                 \
      (head)->slh_first = NULL;                             \
} while (/*CONSTCOND*/0)

#define     SLIST_INSERT_AFTER(slistelm, elm, field) do {               \
      (elm)->field.sle_next = (slistelm)->field.sle_next;         \
      (slistelm)->field.sle_next = (elm);                   \
} while (/*CONSTCOND*/0)

#define     SLIST_INSERT_HEAD(head, elm, field) do {              \
      (elm)->field.sle_next = (head)->slh_first;                  \
      (head)->slh_first = (elm);                            \
} while (/*CONSTCOND*/0)

#define     SLIST_REMOVE_HEAD(head, field) do {                   \
      (head)->slh_first = (head)->slh_first->field.sle_next;            \
} while (/*CONSTCOND*/0)

#define     SLIST_REMOVE(head, elm, type, field) do {             \
      if ((head)->slh_first == (elm)) {                     \
            SLIST_REMOVE_HEAD((head), field);               \
      }                                               \
      else {                                                \
            struct type *curelm = (head)->slh_first;        \
            while(curelm->field.sle_next != (elm))                \
                  curelm = curelm->field.sle_next;          \
            curelm->field.sle_next =                        \
                curelm->field.sle_next->field.sle_next;           \
      }                                               \
} while (/*CONSTCOND*/0)

#define     SLIST_FOREACH(var, head, field)                             \
      for((var) = (head)->slh_first; (var); (var) = (var)->field.sle_next)

/*
 * Singly-linked List access methods.
 */
#define     SLIST_EMPTY(head) ((head)->slh_first == NULL)
#define     SLIST_FIRST(head) ((head)->slh_first)
#define     SLIST_NEXT(elm, field)  ((elm)->field.sle_next)


/*
 * Singly-linked Tail queue declarations.
 */
#define     STAILQ_HEAD(name, type)                         \
struct name {                                               \
      struct type *stqh_first;      /* first element */                 \
      struct type **stqh_last;      /* addr of last next element */           \
}

#define     STAILQ_HEAD_INITIALIZER(head)                         \
      { NULL, &(head).stqh_first }

#define     STAILQ_ENTRY(type)                                    \
struct {                                              \
      struct type *stqe_next; /* next element */                  \
}

/*
 * Singly-linked Tail queue functions.
 */
#define     STAILQ_INIT(head) do {                                \
      (head)->stqh_first = NULL;                            \
      (head)->stqh_last = &(head)->stqh_first;                    \
} while (/*CONSTCOND*/0)

#define     STAILQ_INSERT_HEAD(head, elm, field) do {             \
      if (((elm)->field.stqe_next = (head)->stqh_first) == NULL)  \
            (head)->stqh_last = &(elm)->field.stqe_next;          \
      (head)->stqh_first = (elm);                           \
} while (/*CONSTCOND*/0)

#define     STAILQ_INSERT_TAIL(head, elm, field) do {             \
      (elm)->field.stqe_next = NULL;                              \
      *(head)->stqh_last = (elm);                           \
      (head)->stqh_last = &(elm)->field.stqe_next;                \
} while (/*CONSTCOND*/0)

#define     STAILQ_INSERT_AFTER(head, listelm, elm, field) do {         \
      if (((elm)->field.stqe_next = (listelm)->field.stqe_next) == NULL)\
            (head)->stqh_last = &(elm)->field.stqe_next;          \
      (listelm)->field.stqe_next = (elm);                   \
} while (/*CONSTCOND*/0)

#define     STAILQ_REMOVE_HEAD(head, field) do {                        \
      if (((head)->stqh_first = (head)->stqh_first->field.stqe_next) == NULL) \
            (head)->stqh_last = &(head)->stqh_first;              \
} while (/*CONSTCOND*/0)

#define     STAILQ_REMOVE(head, elm, type, field) do {                  \
      if ((head)->stqh_first == (elm)) {                    \
            STAILQ_REMOVE_HEAD((head), field);              \
      } else {                                        \
            struct type *curelm = (head)->stqh_first;       \
            while (curelm->field.stqe_next != (elm))              \
                  curelm = curelm->field.stqe_next;         \
            if ((curelm->field.stqe_next =                        \
                  curelm->field.stqe_next->field.stqe_next) == NULL) \
                      (head)->stqh_last = &(curelm)->field.stqe_next; \
      }                                               \
} while (/*CONSTCOND*/0)

#define     STAILQ_FOREACH(var, head, field)                      \
      for ((var) = ((head)->stqh_first);                    \
            (var);                                          \
            (var) = ((var)->field.stqe_next))

/*
 * Singly-linked Tail queue access methods.
 */
#define     STAILQ_EMPTY(head)      ((head)->stqh_first == NULL)
#define     STAILQ_FIRST(head)      ((head)->stqh_first)
#define     STAILQ_NEXT(elm, field) ((elm)->field.stqe_next)


/*
 * Simple queue definitions.
 */
#define     SIMPLEQ_HEAD(name, type)                              \
struct name {                                               \
      struct type *sqh_first; /* first element */                 \
      struct type **sqh_last; /* addr of last next element */           \
}

#define     SIMPLEQ_HEAD_INITIALIZER(head)                              \
      { NULL, &(head).sqh_first }

#define     SIMPLEQ_ENTRY(type)                                   \
struct {                                              \
      struct type *sqe_next;  /* next element */                  \
}

/*
 * Simple queue functions.
 */
#define     SIMPLEQ_INIT(head) do {                               \
      (head)->sqh_first = NULL;                             \
      (head)->sqh_last = &(head)->sqh_first;                      \
} while (/*CONSTCOND*/0)

#define     SIMPLEQ_INSERT_HEAD(head, elm, field) do {                  \
      if (((elm)->field.sqe_next = (head)->sqh_first) == NULL)    \
            (head)->sqh_last = &(elm)->field.sqe_next;            \
      (head)->sqh_first = (elm);                            \
} while (/*CONSTCOND*/0)

#define     SIMPLEQ_INSERT_TAIL(head, elm, field) do {                  \
      (elm)->field.sqe_next = NULL;                         \
      *(head)->sqh_last = (elm);                            \
      (head)->sqh_last = &(elm)->field.sqe_next;                  \
} while (/*CONSTCOND*/0)

#define     SIMPLEQ_INSERT_AFTER(head, listelm, elm, field) do {        \
      if (((elm)->field.sqe_next = (listelm)->field.sqe_next) == NULL)\
            (head)->sqh_last = &(elm)->field.sqe_next;            \
      (listelm)->field.sqe_next = (elm);                    \
} while (/*CONSTCOND*/0)

#define     SIMPLEQ_REMOVE_HEAD(head, field) do {                       \
      if (((head)->sqh_first = (head)->sqh_first->field.sqe_next) == NULL) \
            (head)->sqh_last = &(head)->sqh_first;                \
} while (/*CONSTCOND*/0)

#define     SIMPLEQ_REMOVE(head, elm, type, field) do {                 \
      if ((head)->sqh_first == (elm)) {                     \
            SIMPLEQ_REMOVE_HEAD((head), field);             \
      } else {                                        \
            struct type *curelm = (head)->sqh_first;        \
            while (curelm->field.sqe_next != (elm))               \
                  curelm = curelm->field.sqe_next;          \
            if ((curelm->field.sqe_next =                   \
                  curelm->field.sqe_next->field.sqe_next) == NULL) \
                      (head)->sqh_last = &(curelm)->field.sqe_next; \
      }                                               \
} while (/*CONSTCOND*/0)

#define     SIMPLEQ_FOREACH(var, head, field)                     \
      for ((var) = ((head)->sqh_first);                     \
            (var);                                          \
            (var) = ((var)->field.sqe_next))

/*
 * Simple queue access methods.
 */
#define     SIMPLEQ_EMPTY(head)           ((head)->sqh_first == NULL)
#define     SIMPLEQ_FIRST(head)           ((head)->sqh_first)
#define     SIMPLEQ_NEXT(elm, field)      ((elm)->field.sqe_next)


/*
 * Tail queue definitions.
 */
#define     _TAILQ_HEAD(name, type, qual)                         \
struct name {                                               \
      qual type *tqh_first;         /* first element */           \
      qual type *qual *tqh_last;    /* addr of last next element */     \
}
#define TAILQ_HEAD(name, type)      _TAILQ_HEAD(name, struct type,)

#define     TAILQ_HEAD_INITIALIZER(head)                          \
      { NULL, &(head).tqh_first }

#define     _TAILQ_ENTRY(type, qual)                              \
struct {                                              \
      qual type *tqe_next;          /* next element */            \
      qual type *qual *tqe_prev;    /* address of previous next element */\
}
#define TAILQ_ENTRY(type)     _TAILQ_ENTRY(struct type,)

/*
 * Tail queue functions.
 */
#if defined(_KERNEL) && defined(QUEUEDEBUG)
#define     QUEUEDEBUG_TAILQ_INSERT_HEAD(head, elm, field)              \
      if ((head)->tqh_first &&                              \
          (head)->tqh_first->field.tqe_prev != &(head)->tqh_first)      \
            panic("TAILQ_INSERT_HEAD %p %s:%d", (head), __FILE__, __LINE__);
#define     QUEUEDEBUG_TAILQ_INSERT_TAIL(head, elm, field)              \
      if (*(head)->tqh_last != NULL)                              \
            panic("TAILQ_INSERT_TAIL %p %s:%d", (head), __FILE__, __LINE__);
#define     QUEUEDEBUG_TAILQ_OP(elm, field)                             \
      if ((elm)->field.tqe_next &&                          \
          (elm)->field.tqe_next->field.tqe_prev !=                \
          &(elm)->field.tqe_next)                           \
            panic("TAILQ_* forw %p %s:%d", (elm), __FILE__, __LINE__);\
      if (*(elm)->field.tqe_prev != (elm))                        \
            panic("TAILQ_* back %p %s:%d", (elm), __FILE__, __LINE__);
#define     QUEUEDEBUG_TAILQ_PREREMOVE(head, elm, field)                \
      if ((elm)->field.tqe_next == NULL &&                        \
          (head)->tqh_last != &(elm)->field.tqe_next)             \
            panic("TAILQ_PREREMOVE head %p elm %p %s:%d",         \
                  (head), (elm), __FILE__, __LINE__);
#define     QUEUEDEBUG_TAILQ_POSTREMOVE(elm, field)                     \
      (elm)->field.tqe_next = (void *)1L;                   \
      (elm)->field.tqe_prev = (void *)1L;
#else
#define     QUEUEDEBUG_TAILQ_INSERT_HEAD(head, elm, field)
#define     QUEUEDEBUG_TAILQ_INSERT_TAIL(head, elm, field)
#define     QUEUEDEBUG_TAILQ_OP(elm, field)
#define     QUEUEDEBUG_TAILQ_PREREMOVE(head, elm, field)
#define     QUEUEDEBUG_TAILQ_POSTREMOVE(elm, field)
#endif

#define     TAILQ_INIT(head) do {                                 \
      (head)->tqh_first = NULL;                             \
      (head)->tqh_last = &(head)->tqh_first;                      \
} while (/*CONSTCOND*/0)

#define     TAILQ_INSERT_HEAD(head, elm, field) do {              \
      QUEUEDEBUG_TAILQ_INSERT_HEAD((head), (elm), field)          \
      if (((elm)->field.tqe_next = (head)->tqh_first) != NULL)    \
            (head)->tqh_first->field.tqe_prev =             \
                &(elm)->field.tqe_next;                     \
      else                                            \
            (head)->tqh_last = &(elm)->field.tqe_next;            \
      (head)->tqh_first = (elm);                            \
      (elm)->field.tqe_prev = &(head)->tqh_first;                 \
} while (/*CONSTCOND*/0)

#define     TAILQ_INSERT_TAIL(head, elm, field) do {              \
      QUEUEDEBUG_TAILQ_INSERT_TAIL((head), (elm), field)          \
      (elm)->field.tqe_next = NULL;                         \
      (elm)->field.tqe_prev = (head)->tqh_last;             \
      *(head)->tqh_last = (elm);                            \
      (head)->tqh_last = &(elm)->field.tqe_next;                  \
} while (/*CONSTCOND*/0)

#define     TAILQ_INSERT_AFTER(head, listelm, elm, field) do {          \
      QUEUEDEBUG_TAILQ_OP((listelm), field)                       \
      if (((elm)->field.tqe_next = (listelm)->field.tqe_next) != NULL)\
            (elm)->field.tqe_next->field.tqe_prev =         \
                &(elm)->field.tqe_next;                     \
      else                                            \
            (head)->tqh_last = &(elm)->field.tqe_next;            \
      (listelm)->field.tqe_next = (elm);                    \
      (elm)->field.tqe_prev = &(listelm)->field.tqe_next;         \
} while (/*CONSTCOND*/0)

#define     TAILQ_INSERT_BEFORE(listelm, elm, field) do {               \
      QUEUEDEBUG_TAILQ_OP((listelm), field)                       \
      (elm)->field.tqe_prev = (listelm)->field.tqe_prev;          \
      (elm)->field.tqe_next = (listelm);                    \
      *(listelm)->field.tqe_prev = (elm);                   \
      (listelm)->field.tqe_prev = &(elm)->field.tqe_next;         \
} while (/*CONSTCOND*/0)

#define     TAILQ_REMOVE(head, elm, field) do {                   \
      QUEUEDEBUG_TAILQ_PREREMOVE((head), (elm), field)            \
      QUEUEDEBUG_TAILQ_OP((elm), field)                     \
      if (((elm)->field.tqe_next) != NULL)                        \
            (elm)->field.tqe_next->field.tqe_prev =         \
                (elm)->field.tqe_prev;                      \
      else                                            \
            (head)->tqh_last = (elm)->field.tqe_prev;       \
      *(elm)->field.tqe_prev = (elm)->field.tqe_next;             \
      QUEUEDEBUG_TAILQ_POSTREMOVE((elm), field);                  \
} while (/*CONSTCOND*/0)

#define     TAILQ_FOREACH(var, head, field)                             \
      for ((var) = ((head)->tqh_first);                     \
            (var);                                          \
            (var) = ((var)->field.tqe_next))

#define     TAILQ_FOREACH_SAFE(var, head, field, tvar)                  \
      for ((var) = TAILQ_FIRST((head));                     \
          (var) && ((tvar) = TAILQ_NEXT((var), field), 1);        \
          (var) = (tvar))

#define     TAILQ_FOREACH_REVERSE(var, head, headname, field)           \
      for ((var) = (*(((struct headname *)((head)->tqh_last))->tqh_last));    \
            (var);                                          \
            (var) = (*(((struct headname *)((var)->field.tqe_prev))->tqh_last)))

/*
 * Tail queue access methods.
 */
#define     TAILQ_EMPTY(head)       ((head)->tqh_first == NULL)
#define     TAILQ_FIRST(head)       ((head)->tqh_first)
#define     TAILQ_NEXT(elm, field)        ((elm)->field.tqe_next)

#define     TAILQ_LAST(head, headname) \
      (*(((struct headname *)((head)->tqh_last))->tqh_last))
#define     TAILQ_PREV(elm, headname, field) \
      (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))


/*
 * Circular queue definitions.
 */
#if defined(_KERNEL) && defined(QUEUEDEBUG)
#define QUEUEDEBUG_CIRCLEQ_HEAD(head, field)                      \
      if ((head)->cqh_first != (void *)(head) &&                  \
          (head)->cqh_first->field.cqe_prev != (void *)(head))    \
            panic("CIRCLEQ head forw %p %s:%d", (head),           \
                  __FILE__, __LINE__);                      \
      if ((head)->cqh_last != (void *)(head) &&             \
          (head)->cqh_last->field.cqe_next != (void *)(head))           \
            panic("CIRCLEQ head back %p %s:%d", (head),           \
                  __FILE__, __LINE__);
#define QUEUEDEBUG_CIRCLEQ_ELM(head, elm, field)                  \
      if ((elm)->field.cqe_next == (void *)(head)) {              \
            if ((head)->cqh_last != (elm))                        \
                  panic("CIRCLEQ elm last %p %s:%d", (elm), \
                        __FILE__, __LINE__);                \
      } else {                                        \
            if ((elm)->field.cqe_next->field.cqe_prev != (elm))   \
                  panic("CIRCLEQ elm forw %p %s:%d", (elm), \
                        __FILE__, __LINE__);                \
      }                                               \
      if ((elm)->field.cqe_prev == (void *)(head)) {              \
            if ((head)->cqh_first != (elm))                       \
                  panic("CIRCLEQ elm first %p %s:%d", (elm),      \
                        __FILE__, __LINE__);                \
      } else {                                        \
            if ((elm)->field.cqe_prev->field.cqe_next != (elm))   \
                  panic("CIRCLEQ elm prev %p %s:%d", (elm), \
                        __FILE__, __LINE__);                \
      }
#define QUEUEDEBUG_CIRCLEQ_POSTREMOVE(elm, field)                 \
      (elm)->field.cqe_next = (void *)1L;                   \
      (elm)->field.cqe_prev = (void *)1L;
#else
#define QUEUEDEBUG_CIRCLEQ_HEAD(head, field)
#define QUEUEDEBUG_CIRCLEQ_ELM(head, elm, field)
#define QUEUEDEBUG_CIRCLEQ_POSTREMOVE(elm, field)
#endif

#define     CIRCLEQ_HEAD(name, type)                              \
struct name {                                               \
      struct type *cqh_first;       /* first element */           \
      struct type *cqh_last;        /* last element */            \
}

#define     CIRCLEQ_HEAD_INITIALIZER(head)                              \
      { (void *)&head, (void *)&head }

#define     CIRCLEQ_ENTRY(type)                                   \
struct {                                              \
      struct type *cqe_next;        /* next element */            \
      struct type *cqe_prev;        /* previous element */        \
}

/*
 * Circular queue functions.
 */
#define     CIRCLEQ_INIT(head) do {                               \
      (head)->cqh_first = (void *)(head);                   \
      (head)->cqh_last = (void *)(head);                    \
} while (/*CONSTCOND*/0)

#define     CIRCLEQ_INSERT_AFTER(head, listelm, elm, field) do {        \
      QUEUEDEBUG_CIRCLEQ_HEAD((head), field)                      \
      QUEUEDEBUG_CIRCLEQ_ELM((head), (listelm), field)            \
      (elm)->field.cqe_next = (listelm)->field.cqe_next;          \
      (elm)->field.cqe_prev = (listelm);                    \
      if ((listelm)->field.cqe_next == (void *)(head))            \
            (head)->cqh_last = (elm);                       \
      else                                            \
            (listelm)->field.cqe_next->field.cqe_prev = (elm);    \
      (listelm)->field.cqe_next = (elm);                    \
} while (/*CONSTCOND*/0)

#define     CIRCLEQ_INSERT_BEFORE(head, listelm, elm, field) do {       \
      QUEUEDEBUG_CIRCLEQ_HEAD((head), field)                      \
      QUEUEDEBUG_CIRCLEQ_ELM((head), (listelm), field)            \
      (elm)->field.cqe_next = (listelm);                    \
      (elm)->field.cqe_prev = (listelm)->field.cqe_prev;          \
      if ((listelm)->field.cqe_prev == (void *)(head))            \
            (head)->cqh_first = (elm);                      \
      else                                            \
            (listelm)->field.cqe_prev->field.cqe_next = (elm);    \
      (listelm)->field.cqe_prev = (elm);                    \
} while (/*CONSTCOND*/0)

#define     CIRCLEQ_INSERT_HEAD(head, elm, field) do {                  \
      QUEUEDEBUG_CIRCLEQ_HEAD((head), field)                      \
      (elm)->field.cqe_next = (head)->cqh_first;                  \
      (elm)->field.cqe_prev = (void *)(head);                     \
      if ((head)->cqh_last == (void *)(head))                     \
            (head)->cqh_last = (elm);                       \
      else                                            \
            (head)->cqh_first->field.cqe_prev = (elm);            \
      (head)->cqh_first = (elm);                            \
} while (/*CONSTCOND*/0)

#define     CIRCLEQ_INSERT_TAIL(head, elm, field) do {                  \
      QUEUEDEBUG_CIRCLEQ_HEAD((head), field)                      \
      (elm)->field.cqe_next = (void *)(head);                     \
      (elm)->field.cqe_prev = (head)->cqh_last;             \
      if ((head)->cqh_first == (void *)(head))              \
            (head)->cqh_first = (elm);                      \
      else                                            \
            (head)->cqh_last->field.cqe_next = (elm);       \
      (head)->cqh_last = (elm);                             \
} while (/*CONSTCOND*/0)

#define     CIRCLEQ_REMOVE(head, elm, field) do {                       \
      QUEUEDEBUG_CIRCLEQ_HEAD((head), field)                      \
      QUEUEDEBUG_CIRCLEQ_ELM((head), (elm), field)                \
      if ((elm)->field.cqe_next == (void *)(head))                \
            (head)->cqh_last = (elm)->field.cqe_prev;       \
      else                                            \
            (elm)->field.cqe_next->field.cqe_prev =               \
                (elm)->field.cqe_prev;                      \
      if ((elm)->field.cqe_prev == (void *)(head))                \
            (head)->cqh_first = (elm)->field.cqe_next;            \
      else                                            \
            (elm)->field.cqe_prev->field.cqe_next =               \
                (elm)->field.cqe_next;                      \
      QUEUEDEBUG_CIRCLEQ_POSTREMOVE((elm), field)                 \
} while (/*CONSTCOND*/0)

#define     CIRCLEQ_FOREACH(var, head, field)                     \
      for ((var) = ((head)->cqh_first);                     \
            (var) != (const void *)(head);                        \
            (var) = ((var)->field.cqe_next))

#define     CIRCLEQ_FOREACH_REVERSE(var, head, field)             \
      for ((var) = ((head)->cqh_last);                      \
            (var) != (const void *)(head);                        \
            (var) = ((var)->field.cqe_prev))

/*
 * Circular queue access methods.
 */
#define     CIRCLEQ_EMPTY(head)           ((head)->cqh_first == (void *)(head))
#define     CIRCLEQ_FIRST(head)           ((head)->cqh_first)
#define     CIRCLEQ_LAST(head)            ((head)->cqh_last)
#define     CIRCLEQ_NEXT(elm, field)      ((elm)->field.cqe_next)
#define     CIRCLEQ_PREV(elm, field)      ((elm)->field.cqe_prev)

#define CIRCLEQ_LOOP_NEXT(head, elm, field)                       \
      (((elm)->field.cqe_next == (void *)(head))                  \
          ? ((head)->cqh_first)                             \
          : (elm->field.cqe_next))
#define CIRCLEQ_LOOP_PREV(head, elm, field)                       \
      (((elm)->field.cqe_prev == (void *)(head))                  \
          ? ((head)->cqh_last)                              \
          : (elm->field.cqe_prev))

#endif      /* !_SYS_QUEUE_H_ */

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